BFS

from collections import deque
class Solution:
    def bfs(self, adj):
        visited={}
        ans=[]
        q=deque([])
        q.append(0)
        visited[0]=True

        while len(q)>0:
            k=len(q)
            for i in range(k):
                temp=q.popleft()
                ans.append(temp)
                for k in adj[temp]:
                    if visited.get(k,False)==False:
                        visited[k]=True
                        q.append(k)
        return ans